This disclosure relates generally to ion implanters, and more specifically to predicting dose repeatability for an ion implantation of a substrate.
Ion implantation is a standard technique for introducing conductivity-altering impurities into workpieces such as semiconductor wafers (referred to hereinafter as substrates). In a conventional beamline ion implanter, an ion source generates an ion beam and extraction electrodes extract the beam from the source. An analyzer magnet receives the ion beam after extraction and filters selected ion species from the beam. The ion beam passing through the analyzer magnet then enters an electrostatic lens comprising multiple electrodes with defined apertures that allow the ion beam to pass through. By applying different combinations of voltage potentials to the multiple electrodes, the electrostatic lens can manipulate ion energies. A corrector magnet shapes the ion beam generated from the electrostatic lens into the correct form for deposition onto the substrate. A deceleration stage comprising a deceleration lens receives the ion beam from the corrector magnet and further manipulates the energy of the ion beam before it hits the substrate. As the beam hits the substrate, the ions in the beam penetrate the surface of the substrate coming to rest beneath the surface to form a region of desired conductivity.
In semiconductor manufacturing, a beamline ion implanter often has to process many batches of substrates based on various recipes. For batches of substrates processed with a common recipe, it is critical that the ion implanter maintain a consistent ion beam output so that it can deliver a desired dose of ions at the chosen energy and incident angle into the surface of each substrate. Dose repeatability which is a measurement indicative of the ability of an ion implanter to generate a batch of substrates each containing a dose of ions at the chosen energy and incident angle that matches the dose of ions found on the other substrates in the batch. Because the optimal combination of settings for beamline elements (e.g., ion source, extraction electrodes, analyzer magnet, first deceleration stage, corrector magnet, second deceleration stage, etc.) may change from setup to setup due to variations in source conditions or changes in the beamline surface conditions that arise over time, it becomes difficult to obtain an ion implantation for a batch of substrates with a dose repeatability that is satisfactory for the implantation. Consequently, some substrates in the batch may end up having undesired conductivity which can lead to scrapping of the substrates. Currently, there are no approaches that enable ion implanters to predict dose repeatability for ion implantations.